Any publications or references discussed herein are presented to describe the background of the invention and to provide additional detail regarding its practice. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.
Silicone-hydrogel films are used to make extended wear soft contact lenses due to their high oxygen permeability, flexibility, comfort and reduced corneal complications. Conventional hydrogel materials (e.g. HEMA), by themselves have poor oxygen permeability and they transport oxygen to the eye through the absorbed water molecules. Water itself has a low Dk value (80 barrer). 1 Barrer=10−11 (cm3 O2) cm cm−2 s−1 mmHg−1 where ‘cm3 O2’ is at a quantity of oxygen at standard temperature and pressure and where ‘cm’ represents the thickness of the material and cm−2 is the reciprocal of the surface area of that material. Lenses made from conventional hydrogel materials, upon exposure to atmospheric air for long periods, get slowly dehydrated and the amount of oxygen transported to the cornea is reduced, which leads to eye irritation, redness and other corneal complications, all of which restrict their use for extended periods of wear.
Silico ne-hydrogels with the comfort of soft contact lenses and significantly higher oxygen permeability overcame these obstacles for extended wear and were revolutionary in the field of ophthalmic lenses. The following patents describe silicone-hydrogels for use in extended wear contacts all of which are incorporated herein in their entirety by reference. U.S. Pat. Nos. 4,954,587; 5,010,141; 5,079,319; 5,115,056; 5,260,000; 5,336,797; 5,358,995; 5,387,632; 5,451,617; 5,486,579 and 5,998,498.
U.S. Pat. No. 3,808,178 claims compositions prepared by copolymerization of a poly-siloxanylalkyl acrylic ester and an alkyl acrylic ester for the production of contact lenses with increased oxygen permeability. The compositions disclosed (see Columns 2 and 3) have trisiloxane (Si—O—Si—O—Si) and siloxycarbo (Si—O—C) linkages, which are susceptible to hydrolysis in spite of the presence of sterically hindered groups attached to silicon.
The polymer obtained by copolymerizing 3-[tris(trimethylsiloxy)silyl]propyl methacrylate (usually abbreviated TRIS), [(CH3)3SiO]3Si(CH2)3OOCC(CH3)═CH2, and N,N-dimethylacrylamide, H2C═CHCON(CH3)2, is disclosed in U.S. Pat. Nos. 5,358,995 and 5,387,632, both of which are incorporated herein in their entirety by reference, as a hydrogel composition useful for preparing ophthalmic lenses with good wettability and oxygen permeability. However, if a carboxylic acid such as methacrylic acid is included in the copolymerization to improve the water content of the product, the composition is gradually hydrolyzed and contact lenses made from it degrade when stored in aqueous media. U.S. Pat. No. 3,377,371 and US 2008/0081894 A1, both of which are incorporated herein in their entirety by reference, disclose use of sterically hindered derivatives of TRIS to forestall this type of degradation. However, the continued presence of siloxycarbo (Si—O—C—) and/or trisiloxane (Si—O—Si—O—Si) units in the compositions makes them susceptible to hydrolysis. U.S. Pat. No. 4,260,725 and U.S. Pat. No. 4,259,467, both of which are incorporated herein in their entirety by reference, disclose hydrolytically stable contact lens comprising polysiloxane-containing hydrophilic side chains. The disclosed polysiloxane monomers are bifunctional in nature and have —Si—C linkages instead of —Si—O—C— bonds in terminal positions. However, in the lens industry mono-functional monomers are preferred more than multi-functional monomers as they give better control of the modulus of the final lens material. The instant invention discloses mono-functional monomers comprising carbosiloxane linkages (for example, Si—CH2CH2—Si and Si—CH2—CH2—Si—O—Si) to avoid the material degradation problems attendant to hydrolysis, while at the same time providing better surface wettability and oxygen permeability to films, lenses and other objects made from said monomers.
Carbosiloxanes contain both the —Si(CHR)x—Si— and —Si—O—Si— functionalities. R is hydrogen or a hydrocarbyl group such as an alkyl, cycloalkyl or aryl group. The subscript x is an integer greater than or equal to 1. Use of carbosiloxanes to impart hydrolysis resistance to surfactants in agricultural and other topical formulations is disclosed in U.S. Pat. Nos. 7,700,797 B2 and 7,507,775 B2, both of which are incorporated herein in their entirety by reference. The instant invention discloses the acrylate and methacrylated carbosiloxane monomers, having improved hydrolysis resistance, that can be copolymerized with unsaturated hydrophilic monomers, such as N-vinyl pyrrolidone and N,N-dimethylacrylamide, to produce silicone hydrogels suitable for ophthalmic lenses.
In their study of gas permeability through silicone polymer membranes, Stern, et al (J. Polymer Science Part B: Polymer Physics 25 (1987) 1263-1298) reported that substitution of methyl groups by bulky groups (e.g., ethyl, isopropyl, butyl, hexyl) on the silicone backbone, or the replacement of siloxane (—SiOSi—) linkage by carbosilane (—Si(CH2)nSi—) linkage resulted in reduced oxygen permeability. Based on Stern et al report, one would expect the oxygen permeability to get reduced when siloxane linkage (—Si—O—Si) is replaced by carbosiloxane linkage (—Si(CH2)nSi—) in the backbone chain. Surprisingly, the silicone hydrogel film produced using the carbosiloxane monomer of the current invention showed improved oxygen permeability in comparison to the corresponding siloxane monomer having conventional siloxane linkage.
The instant invention provides carbosiloxane monomers and polymers derived there from that satisfy the deficiencies that exist in current state-of-the-art products and technologies.